in which \(\phi _l\)  represents the dimerization at the \(l\) th site and
an alternating sign of the hopping elements reflects dimerization
between the carbon atoms in the molecule. Without the loss of
generality, it is convenient to neglect the kinetic energy in the
system and take \(\phi _l=\phi \) , \(t=1\)  [1]}. There is a
critical point at \(\phi =0\)  ,which divides the ground states into two
different types. One should point out that SSH has a gaped
excitation for any \(\phi \in [-1,1]\)  and the quantum phase transition
comes from the excitation of the boundary states[1]}.
